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Some aspects of the acid dissolution of hematite Bath, Murray Damon

Abstract

The dissolution of hematite (⍺ -Fe203) in hydrochloric acid solutions has been investigated. Sintered compacts, single crystals and particulate specimens were subjected to leaching over a range of temperatures and acid concentrations. The effects of varying the hydrogen and chloride ion concentrations independently were also investigated. The dissolution was found to be highly anisotropic, the basal (0001) plane dissolving at a rate an order of magnitude greater than that of any of the other surfaces examined. Qualitative experiments indicated that this effect is also characteristic of dissolution in nitric, sulphuric and perchloric acids. The effect is attributed to the presence of a greater number of active dissolution sites on the basal plane, resulting from the anisotropic nature of the hematite crystal structure, and possibly also from the presence of a greater number of dislocations terminating on the basal plane. The reaction rate was found to depend strongly on the acid concentration, increasing as the 2.5th power of the acid normality in the range 0.2-7.ON, an to vary independently with hydrogen and chloride ion concentrations. At acidities below 2N, the rate appears to vary with the product of hydrogen and chloride ion activities, while at concentrations in the range 2-7N, a linear dependence on hydrogen ion activity was observed. A tentative mechanism is proposed, in which protonation of the hydrated oxide surface is followed by adsorption of a chloride ion and desorption of a ferric-chloride complex.

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